This invention relates generally to the field of collapsible reusable shipping containers of types commonly used for transporting bulk and particulate materials, and more particularly to an improved reinforcing insert for use in conjunction therewith. Containers of this general type are well known in the art, as are corresponding reinforcing inserts therefor, and the invention lies in specific constructional details which permit the obtaining of increased mechanical strength and bursting resistance without corresponding increase in weight and materials. Mention is made of my prior U.S. Pat. Nos. 3,443,737, granted Apr. 13, 1969; and 4,252,266, granted Feb. 24, 1981. Particular reference is made to my copending application, Ser. No. 06/257,106 (now U.S. Pat. No. 4,358,049).
Shipping containers of this type are primarily used for air and truck transport, where space and weight considerations are of greater importance than the cost of fabrication. In the latter of my above mentioned patents, there is disclosed an improved form in which the conventional wood or synthetic resinous pallet has been substituted by an integral base element which not only saves a substantial amount of cargo space in the transporting vehicle, but provides a degree of rigidity to the device which is more than adequate for most loads provided that the container is not of excessive size.
While the base element provides such rigidity as a result of the gluing of foldable tabs integrally formed with the lower edges of the side walls, and the side walls themselves possess substantial tensil and compressive strength in the plane thereof, when such devices are used for the transportation of relatively heavy particulate loads, the side walls of the container do not always exhibit the desired degree of resistance to outward bulging in response to stresses exerted by the load in planes normal to the planes of the side wall. Under such circumstances, it is possible to increase the thickness of the side walls. However, where more than two plys of corrugation are involved, it becomes increasingly difficult to fold the walls in a manner necessary to place the container in collapsed condition for return to the shipping source. The above mentioned copending application disclosed a collapsible reinforcing element or liner which can be separated from the main body of the container to provide, in a separable, foldable element the necessary additional mechanical strength. However, the disclosed liner is formed of three or more plys of corrugated material, and is not without substantial thickness and weight. With ever increasing freight tariffs, there has been a growing need for lighter weight reinforcing or liner elements which provide substantially the same degree of mechanical strength.